This invention relates to novel mixtures of compounds and, in particular, novel mixtures that exist as discotic liquid crystals and which have significantly improved liquid crystal and conductive properties. The invention also relates to certain novel compounds per se.
Several potential applications of discotic liquid crystals which are based on a combination of their processability and their ability to act as semiconductors have already been described. These include their use as (1) conducting interconnects in stacked silicon chip systems (2) as conducting layers in photoreproductive and electrophotographic systems (3) as active elements in electronic xe2x80x98nosexe2x80x99 arrays (4) as conductive elements in spatial light modulators and many others and as (5) electron/hole transporting materials in light emitting diodes.
Thus according to the main feature of the invention we provide a mixture comprising a molecule of formula I; 
in which A1, A2, A3, A4, A5 and A6, which may be the same or different, are each N or xe2x80x94CH;
Y1, Y2, Y3, Y4, Y5 and Y6, which may be the same or different, are each hydrogen or C1 to C12 alkoxy;
X1, X2, X3, X4, X5 and X6, which may be the same or different, are each hydrogen, C1 to C12 alkoxy or alkyl C1 to C12; and
R7, R8, R9, R10, R11 and R12 are each hydrogen, or each of R7 and R8, R9 and R10 and R11, and R12 may form a bond;
and a molecule of formula II; 
in which R1, R2, R3, R4, R5 and R6, which may be the same or different, are each alkyl or substituted (and/or chiral) alkyl C1 to C16, acyl C1 to C16, polyethyleneoxy, a flexible connection to a polymer backbone or part of a polymer backbone in homopolymers, copolymers or block copolymers; and
B1, B2, B3, B4, B5 and B6 a, which may be the same or different, are each, hydrogen, alkyl C1 to C16, alkoxy C1 to C16, nitro, halogeno, cyano, amido, diazo or ester, e.g. alkyl C1 to C16 ester.
By the term xe2x80x9cmixturexe2x80x9d we mean a combination of compounds of formula I and formula II. In such combinations, quadrupolar attractions and van der Waals forces, between compounds of formula I and compounds of formula II suggests that the mixtures exist as compounds per se. Thus, any reference to mixtures of compounds of formula I and II should be construed accordingly.
In a preferred mixture of the invention, in the compound of formula I each of A1, A2, A3, A4, A5 and A6 are the same.
When each of A1, A2, A3, A4, A5 and A6 is N, then each of Y1, Y2, Y3, Y4, Y5 and Y6 preferentially represents hydrogen or alkoxy C3 to C8. Further, when each of A1, A2, A3, A4, A5 and A6 is N, then each of X1, X2, X3, X4, X5 and X6 is preferably C2 to C12 alkyl or C4 to C12 alkoxy, more preferably C6 to C9 alkyl or C6 to C9 alkoxy. Most preferably, when each of A1, A2, A3, A4, A5 and A6 is N, then each of X1, X2, X3, X4, X5 and X6 is either C9 alkyl or C6 alkoxy. We especially prefer each of X1, X2, X3, X4, X5 and X6 to be the same C9 alkyl or each of X1, X2, X3, X4, X5 and X6 to be the same C6 alkoxy.
When each of A1, A2, A3, A4, A5 and A6 is N, especially preferred mixtures are those in which each of Y1, Y2, Y3, Y4, Y5 and Y6 is hydrogen and each of X1, X2, X3, X4, X5 and X6 is C9 alkyl, or, alternatively, each of Y1, Y2, Y3, Y4, Y5 and Y6 is C6 alkoxy and each of X1, X2, X3, X4, X5 and X6 is C6 alkoxy.
When each of A1, A2, A3, A4, A5 and A6 is Cxe2x80x94H, then each of Y1, Y2, Y3, Y4, Y5 and Y6 preferentially represents hydrogen or alkoxy C3 to C8, preferably hydrogen or alkoxy C5 to C7 and most preferably hydrogen or alkoxy C6.
When each of A1, A2, A3, A4, A5 and A6 is Cxe2x80x94H, then each of X1, X2, X3, X4, X5 and X6 is C2 to C12 alkyl or C2 to C12 alkoxy. When each of X1, X2, X3, X4, X5 and X6 is alkoxy, they are preferably C6 to C12 alkoxy.
Preferred mixtures are those in which compounds of formula I are compounds of formula III; 
in which X1, X2, X3, X4, X5 and X6 are each the same and are selected from xe2x80x94C9H19, xe2x80x94C12H25, xe2x80x94OC6H13 and xe2x80x94OC11H23; and
each of Y1, Y2, Y3, Y4, Y5 and Y6 are each the same and are selected from hydrogen and xe2x80x94OC6H13.
Further preferred mixtures are those in which the compounds of formula I are compounds of formula IV; 
in which X1, X2, X3, X4, X5 and X6 are each the same and are selected from xe2x80x94C9H19, and xe2x80x94OC6H13; and
each of Y1, Y2, Y3, Y4, Y5 and Y6 are each the same and are selected from hydrogen and xe2x80x94OC6H13.
In a preferred mixture of the invention, in the molecule of formula II each of R1, R2, R3, R4, R5 and R6 are the same and B1, B2, B3, B4, B5 and B6 are hydrogen. Preferably, each of R1, R2, R3, R4, R5 and R6 are alkyl C3 to C16, more preferably alkyl C4 to C11 and most preferably C6 or C11 alkyl. The most preferred compounds of formula II are 2,3,6,7,10,11-hexahexyloxytriphenylene and 2,3,6,7,10,11-hexaundecyloxytriphenylene.
A further preferred mixture of the invention, contains the compound of formula II in which each of R1, R2, R3, R4, R5 and R6 are the same and are alkyl C3-C16, more preferably C4-C11 alkyl and most preferably C6 alkyl. B1, B2, B3, and B4 are hydrogen and B5 and B6 are the same or different and are each or both hydrogen or fluorine. Most preferable is the compound formed by the mixture of formula I with formula II in which formula II is 1,4-difluoro-2,3,6,7,10,11-hexahexyloxytriphenylene. These mixtures are advantages in that the mesophase persists well below room temperature.
Liquid crystal phases can be induced in non-mesogenic materials such as those of formula II in which each of R1, R2, R3, R4, R5 and R6 are the same or different and are alkyl C2-C11 or ethyleneoxy C3-C9. More preferably when R1, R2, R3, R4, R5 and R6 are the same and ethyleneoxy C5, and when R1, R2, R3, R4, R5 and R6 are a combination of ethyleneoxy C5 and alkyl C6. Most preferably when formula II is 2-(1,4,7-Trioxaoctyl)-3,6,7,10,11-pentahexyloxytriphenylene, 2,7-Di(1,4,7-trioxaoctyl)-3,6,10,11-tetrahexyloxytriphenylene, 2,7,10-Tri(1,4,7-trioxaoctyl)-3,6,11-trihexyloxytriphenylene or 2,3,6,7,10,11-Hexa(1,4,7-trioxaoctyl)triphenylene.
A preferred mixture contains a polythene main chain polymer with formula II as a side chain substituent in the form shown in formula V. X is alkyl C1-C10 or an ether oxygen linkage (xe2x80x94Oxe2x80x94), and R is hydrogen or methyl. Addition of molecules of formula I to polymers such as those in Formula V produces a liquid crystal polymer which shows much better alignment properties than the polymer of formula V alone.
A further preferred mixture contains formula II as a functionality in polystyrene block copolymers of the form shown in formula VI. The ratio of n:m is from 6-18:1. The compound formed with formula I is again easier to align than the polymer of formula V alone with the added advantage that the blocks comprising the copolymer undergo micro-phase separation. 
Another preferred mixture contains the formula I as a constituent part of the polymer backbone, the length of the flexible spacer n is between 6 and 18, most preferably 6, 12, and 18 and the number of molecules of formula II per polymer formula VII, m, is between 2 and 1000.
Block copolymers containing blocks of polyethylene oxide and blocks of formula VII can also be made to undergo micro-phase separation and further preferred mixtures contain the polymer of formula VIII. Where the number of molecules of formula I (m) is 10-100 and the number of ethyleneoxide groups in the side chains (n) is 200-500
In the mixture of the invention, specific compounds of formula I which may be mentioned include the following;
2,3,6,7,10,11-hexakis(4-n-nonylphenyl)dipyrazine[2,3-f:2xe2x80x2,3xe2x80x2-h]quinoxaline;
2,3,6,7,10,11-hexakis-(3,4-dehexyloxyphenyl)dipyrazino[2,3-f:2xe2x80x23xe2x80x2-h]quinoxaline;
2,3,6,7,10,11-hexakis-4(-n-nonylphenyl)-triphenylene;
2,3,6,7,10,11-hexakis-(4-n-dodecylphenyl)triphenylene;
2,3,6,7,10,11-hexakis-(4-n-hexyloxy-phenyl)-triphenylene;
2,3,6,7,10,11-hexakis-(4-n-undecyloxy-phenyl)-triphenylene;
2,3,6,7,10,11-hexakis-(3,4-n-dihexyloxy-phenyl)-triphenylene; and
2,3,8,9,12,13,18,19,22,23,28,29-dodecakis(hexyloxy)hexabenz[a,c,k,m,v,w]trinaphthylene.
In the mixture of the invention, specific compounds of formula II which may be mentioned include the following;
2,3,6,7,10,11-hexahexyloxytriphenylene,
2,3,6,7,10,11-hexaundecyloxytriphenylene,
1,4-difluoro-2,3,6,7,10,11-hexahexyloxytriphenylene,
2-(1,4,7-trioxaoctyl)-3,6,7,10,11-pentahexyloxytriphenylene,
2,7-di(1,4,7-trioxaoctyl)-3,6,10,11-tetrahexyloxytriphenylene,
2,7,10-tri(1,4,7-trioxaoctyl)-3,6,11-trihexyloxytriphenylene,
2,3,6,7,10,11-hexa(1,4,7-trioxaoctyl)triphenylene,
acetic acid 2-hydroxy-3,6,7,10,11-pentahexyloxytriphenylene ester,
hexanoic acid 2-hydroxy-3,6,7,10,11-pentahexyloxytriphenylene ester,
4-biphenylcarboic acid 2-hydroxy-3,6,7,10,11-pentahexyloxytriphenylene ester,
4-nitrobenzoic acid 2-hydroxy-3,6,7,10,11-pentahexyloxytriphenylene ester,
3,5-dinitrobenzoic acid 2-hydroxy-3,6,7,10,11-pentahexyloxytriphenylene ester,
4-cyanobenzoic acid 2-hydroxy-3,6,7,10,11-pentahexyloxytriphenylene ester,
4-fluorobenzoic acid 2-hydroxy-3,6,7,10,11-pentahexyloxytriphenylene ester,
1-naphthoic acid 2-hydroxy-3,6,7,10,11-pentahexyloxytriphenylene ester,
2-naphthoic acid 2-hydroxy-3,6,7,10,11-pentahexyloxytriphenylene ester,
polythenes bearing formula II as a side chain substituent (formula V),
polyacrylates bearing formula II as a side chain substituent (formula VI
polymers containing formula II as part of the polymer backbone (formula VII),
block copolymers containing a central core of polymer with formula II as part of the polymer backbone surrounded by blocks of poly(ethyleneoxide) with molecular weights in the range 750-2000 (formula VIII).
Thus the most preferred mixtures of the invention are mixtures comprising a compound of formula I selected from the group;
2,3,6,7,10,11-hexakis(4-nonylphenyl)dipyrazine[2,3-f:2xe2x80x2,3xe2x80x2-h]quinoxaline;
2,3,6,7,10,11-hexakis-(4-nonylphenyl)-triphenylene;
2,3,6,7,10,11-hexakis-(4-dodecylphenyl)triphenylene;
2,3,6,7,10,11-hexakis-(4-hexyloxy-phenyl)-triphenylene;
2,3,6,7,10,11-hexakis-(4-n-undecyloxy-phenyl)-triphenylene;
and a compound of formula II selected from the group;
2,3,6,7,10,11-hexahexyloxytriphenylene,
2,3,6,7,10,11-hexaundecyloxytriphenylene,
1,4-difluoro-2,3,6,7,10,11-hexahexyloxytriphenylene,
2-(1,4,7-trioxaoctyl)-3,6,7,10,11-pentahexyloxytriphenylene,
2,7-di(1,4,7-trioxaoctyl)-3,6,10,11-tetrahexyloxytriphenylene,
2,7,10-tri(1,4,7-trioxaoctyl)-3,6,11-trihexyloxytriphenylene,
2,3,6,7,10,11-hexa(1,4,7-trioxaoctyl)triphenylene,
acetic acid 2-hydroxy-3,6,7,10,11-pentahexyloxytriphenylene ester,
hexanoic acid 2-hydroxy-3,6,7,10,11-pentahexyloxytriphenylene ester,
4-biphenylcarboic acid 2-hydroxy-3,6,7,10,11-pentahexyloxytriphenylene ester,
4-nitrobenzoic acid 2-hydroxy-3,6,7,10,11-pentahexyloxytriphenylene ester,
3,5-dinitrobenzoic acid 2-hydroxy-3,6,7,10,11-pentahexyloxytriphenylene ester,
4-cyanobenzoic acid 2-hydroxy-3,6,7,10,11-pentahexyloxytriphenylene ester,
4-fluorobenzoic acid 2-hydroxy-3,6,7,10,11-pentahexyloxytriphenylene ester,
1-naphthoic acid 2-hydroxy-3,6,7,10,11-pentahexyloxytriphenylene ester,
2-naphthoic acid 2-hydroxy-3,6,7,10,11-pentahexyloxytriphenylene ester,
1,4-difluoro-2,3,6,7,10,11-hexakis(hexyloxy)triphenylene, and
polythenes bearing formula II as a side chain substituent (formula V),
polyacrylates bearing formula II as a side chain substituent (formula VI
polymers containing formula II as part of the polymer backbone (formula VII),
block copolymers containing a central core of polymer with formula II as part of the polymer backbone surrounded by blocks of poly(ethyleneoxide) with molecular weights in the range 750-2000 (formula VIII).
The compounds of formula I are novel per se.
Thus, according to a further feature of the invention we provide a compound of formula I 
in which A1-6, X1-6, Y1-6 and R7-12 are as defined above;
provided that the compound of formula I is not 2,3,6,7,10,11-hexakis(4-n-nonylphenyl)dipyrazine[2,3,-f:2,3-h]quinoxaline.
The compounds of formula I are especially advantageous in that they may be mixed with compounds of formula II to form novel compounds which possess properties as, inter alia, highly ordered and highly conducting liquid crystals.
Certain compounds of formula II are also novel per se.
Thus according to the invention we also provide a novel compound of formula II selected from the group;
1,4-difluoro-2,3,6,7,10,11-hexahexyloxytriphenylene,
2-(1,4,7-trioxaoctyl)-3,6,7,10,11-pentahexyloxytriphenylene,
2,7-di(1,4,7-trioxaoctyl)-3,6,10,11-tetrahexyloxytriphenylene,
2,7,10-tri(1,4,7-trioxaoctyl)-3,6,11-trihexyloxytriphenylene,
acetic acid 2-hydroxy-3,6,7,10,11-pentahexyloxytriphenylene ester,
hexanoic acid 2-hydroxy-3,6,7,10,11-pentahexyloxytriphenylene ester,
4-biphenylcarboic acid 2-hydroxy-3,6,7,10,11-pentahexyloxytriphenylene ester,
4-nitrobenzoic acid 2-hydroxy-3,6,7,10,11-pentahexyloxytriphenylene ester,
3,5-dinitrobenzoic acid 2-hydroxy-3,6,7,10,11-pentahexyloxytriphenylene ester,
4-cyanobenzoic acid 2-hydroxy-3,6,7,10,11-pentahexyloxytriphenylene ester,
4-fluorobenzoic acid 2-hydroxy-3,6,7,10,11-pentahexyloxytriphenylene ester,
1-naphthoic acid 2-hydroxy-3,6,7,10,11-pentahexyloxytriphenylene ester,
1,4-difluoro-2,3,6,7,10,11-hexakis(hexyloxy)triphenylene, and
block copolymers containing a central core of polymer with formula II as part of the polymer backbone surrounded by blocks of poly(ethyleneoxide) with molecular weights in the range 750-2000 (formula VIII).
According to the invention we also provide a process for the manufacture of a compound of formula I which comprises reacting a hexahalotriphenylene or a hexahaloquinoxaline with a boronic ester of formula V; 
Synthesis of the quinoxalines involves a straightforward condensation of hexaaminobenzene with the appropriate benzil but to make the hexakis (4-alkoxyphenyl) triphenylenes a variation on the normal Suzuki reaction conditions had to be employed. The conditions required for this type of polyarylation are more demanding than those for simple arylxe2x80x94aryl coupling. Under standard Suzuki coupling conditions (0.3 mol % Pd(0) as Pd(PPh3)4, toluene, water Na2CO3, reflux under argon for 24 hours) the reaction of the appropriate aryl boronic acid with hexabromotriphenylene gave the product formula III contaminated with a reduction product. Competitive reduction under these reaction conditions is a well-known problem. Ordinarily it is not significant since it often only amounts to only 1-2% and the by-product is usually easily removed. However, in this case the by-product is very difficult to remove and the xe2x80x9cerror is cumulativexe2x80x9d giving 5-12% of the reduction product. To overcome this problem we have modified the Suzuki protocol to minimise reduction. A stronger base was used to improve the rate of metathesis of the boronic acid species and DME was used to give a homogenous reaction medium. In order to prevent excessive de-borylation of the boronic acid starting material, the less labile pinacol ester (above) was used. This ester is also easier to purify (by distillation or column chromatography) than the acid and is more stable with respect to temperature, pH and oxygen. These modifications improved the yield and purity of formula III giving a product in which the by-product could no longer be detected by 1H NMR.
The pioneering work of the group of Mullen suggested that oxidative cyclisation of compounds of formula I should yield systems with exceptionally large aromatic cores. This was achieved using dichloromethane/FeCl3 followed by a reductive methanol work up and excellent yields were obtained (70%, 2 hrs at 25xc2x0 C.). This is a new type of polynuclear aromatic core.
We also provide a method of manufacturing a mixture and or a liquid crystal as hereinbefore described which comprises mixing a compound of formula I with a compound of formula II.
2,3,6,7,10,11-hexahexyloxytriphenylene is known to display a hexagonal columnar mesophase between about 70 and 100xc2x0 C. However the novel mixtures of the invention comprising a compound of formula II, e.g. 2,3,6,7,10,11-hexahexyloxytriphenylene, and a compound of formula I form a novel liquid crystal with a hexagonal columnar phase at a higher temperature than 2,3,6,7,10,11-hexahexyloxytriphenylene alone. Thus, for example, a mixture of 2,3,6,7,10,11-hexahexyloxytriphenylene and 2,3,6,7,10,11-hexakis(4-nonylphenyl)dipyrazine[2,3-f:2xe2x80x2,3xe2x80x2-h]quinoxaline form a novel liquid crystal with a hexagonal columnar phase at a temperature of between 130 and 240xc2x0 C.
The mesophase properties are altered by changing the properties of either formula I or formula II possible combinations of which were discussed earlier. The properties of a selection of the most preferable combinations of formula I and formula II are shown in Table 1.
Thus according to a further feature of the present invention we provide a liquid crystal with a hexagonal columnar phase between temperatures of less than room temperature and 280xc2x0 C. The low temperature phase of many of the mixtures is glassy, allowing the columnar order of the mesophase to persist at low temperature without the introduction of crystalline defects.
The liquid crystal of the invention especially comprises a mixture of compounds of formula I and formula II as hereinbefore described.
In the mixtures and liquid crystals of the invention the ratio of the compound of formula I and formula II may vary. However, it is preferred that the ratio is substantially 50:50.
The unit cell parameters for the some of these mixtures are given in Table II.
The fact that there is a single column/column repeat distance and a hexagonal lattice shows that there cannot be segregated stacks of compounds of formula I and formula II. Thus there is an alternating stack structure in which a compound of formula I is stacked on a compound of formula II and so on.
Thus according to a further feature of the invention we provide a liquid crystal as hereinbefore described which has an alternating stack structure. We especially provide a liquid crystal which comprises an alternating stack of compounds of formula I and formula II.
In relation to the entries displayed in Table I it is important to note that:
1) There is 1:1 compound formation in the mixture of compounds of formula I and formula II. That the temperature of the clearing temperature of the 1:1 compound is generally above that of the individual components and that this 1:1 compound undergoes isothermal phase transitions. A specific example is given in FIG. 1 (the phase/composition diagram of HAT6 (2,3,6,7,10,11-hexahexyloxytriphenylene)+PDQ9 (2,3,6,7,10,11-hexakis(4-n-nonylphenyl)dipyrazine[2,3-f.2xe2x80x2,3xe2x80x2-h]quinoxaline)
2) There may be induction of liquid crystalline behaviour. The 1:1 compounds give columnar liquid crystal phases whereas the individual components of formula I and formula II may either be mesogenic or non-mesogenic. Preferable examples are 2,3,6,7,10,11-Hexa(1,4,7-trioxaoctyl)triphenylene and 2-Naphthoic acid 2-hydroxy-3,6,7,10,11-pentahexyloxytriphenylene ester.
3) In the use of polymer derivatives of formula II 1:1 compounds with formula I are often easier to align by surface or shear interactions than the polymers on their own. Hence FIG. 2 shows the alignment of the mixture of Formula VII (n=12) with (2,3,6,7,10,11-hexakis(4-n-nonylphenyl)dipyrazine[2,3-f:2xe2x80x2,3xe2x80x2-h]quinoxaline) compared to that of the polymer alone.
4) In the case of block copolymers of compound formula VIII, addition of the compound of formula I can induce microphase separation, for example when Formula VIII (n=40) is mixed with 2,3,6,7,10,11-hexakis(4-n-nonylphenyl)dipyrazine[2,3-f:2xe2x80x2,3xe2x80x2-h]quinoxaline.
5) These new mixtures show enhanced conductive behaviour. Studies on the photoconductivity of 2,3,6,7,10,11-hexahexyloxytriphenylene have found that there exist clear hole transits in the mesophase while the transient photocurrent displayed a featureless decay in the crystalline phase. Holes in the mesophase of that material were found to have a mobility of xcexcxcfx80=3.0xc3x9710xe2x88x924 cm2Vxe2x88x921sxe2x88x921, which is generally a 200 fold enhancement over known liquid crystals. Detailed analysis of the featureless photocurrent transient decays demonstrated that the columnar stacks behave like one dimensional semiconductors and that the holes had a range of S=4 xcexcm before deep trapping in the crystalline phase. Thus discotics have already been demonstrated as hole transporting layers. The liquid crystals of the invention demonstrate improved hole mobility and hole range by using a mixture designed to give favourable xcfx80-stacking. Thus the liquid crystals of the invention have an enhanced conductivity over known liquid crystals, with an enhancement factor of from 10 to 105 
For sandwich samples of thickness 25 xcexcm, of 2,3,6,7,10,11-hexaundecyloxytriphenylene (HAT11) the photocurrent is not detectable in either the discotic or crystalline phase. This places an upper limit on the peak photocurrent, Ip of Ip less than  less than 4xc3x9710xe2x88x927 A even at the highest applied electric fields of E=6.0MVmxe2x88x921. This is in stark contrast to the photoconductivity of 2,3,6,7,10,11-hexahexyloxytriphenylene where the magnitude of the peak photocurrent in the discotic phase at similar electric field and sample thickness was Ip=10xe2x88x925 A.
With 1:1 mixture of 2,3,6,7,10,11-hexaundecyloxytriphenylene and 2,3,6,7,10,11-hexakis-(4-nonylphenyl)-triphenylene however, there is a transient photocurrent generated by a thin sheet of positive carriers of thickness, xcex4xe2x80x940.1 xcexcm travelling from a top electrode, where they are generated by a laser pulse, to a bottom counter electrode under the influence of an electric field (FIG. 3).
Taking a mobility of 0.017 cm2Vxe2x88x921sxe2x88x921, as representative of the discotic phase, it is noteworthy that in the system of the invention the mobility has increased, by a factor ≈57, in comparison to that previously found for HAT11. Also of interest is the observation in the mixture of a clear transit even in the low temperature regime. From the pre transit time photocurrent decay it is possible to estimate a trapping time and a consequent carrier schubweg and the increased mobility are indicative of a great improvement in the ordering of the columnar stacks in the mixed system. This ordering is a direct consequence of the mixture as 2,3,6,7,10,11-hexakis-(4-nonylphenyl)-triphenylene alone does not photoconduct. Ordering has been found elsewhere to lead to higher mobility in compounds forming a helical columnar phase and to dominate the mobility parallel to the column in hexagonal phases. Therefore, according to a yet further feature of the invention we provide a liquid crystal which has enhance hole electron mobility and charge carrier schubweg.
Conductivity in these systems has also been investigated by sandwiching a homeotropic film of the mixtures between conducting ITO coated glass electrodes. FIG. 4 shows the IV characteristics of 2,3,6,7,10,11-hexakis-(4-nonylphenyl)-triphenylene, 2,3,6,7,10,11-hexahexyloxytriphenylene and their 1:1 mixture
FIG. 5 shows the frequency dependent AC conduction properties of the mixture before and after the sample cell is annealed by the action of heat and applied field. Typically the annealing process is carried out in the liquid crystalline phase of the mixture, a field is then applied, the intensity of which is steadily increased until the resistance of the sample begins to suddenly fall (typically 20V across a 6 xcexcm cell).
We also provide the use of a mixture of a compound of formula I and a compound of formula II in the manufacture of a liquid crystal as hereinbefore described.
We further provide the use of a compound of formula I in the manufacture of a mixture or a liquid crystal as hereinbefore described.
We yet further provide the use of a compound of formula II in the manufacture of a mixture or a liquid crystal as hereinbefore described.
The invention will now be described by way of example only.